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Home , Ammonitida, Ammonoidea, Belemnotheutis, Siphuncle, Spirula

Journal of Life Sciences 12 (2018) 30-46 D doi: 10.17265/1934-7391/2018.01.004 DAVID PUBLISHING

The Origin of spirula (Linne, 1758)

E. O. Heyfetz Nachman mi Braslaw 14/3, Yaffo 6808998, Israel

Abstract: The article presents evidence regarding the origin of Spirula from spiral-shelled forms. The geological age of the is revised from the Miocene to the . The causes of the reorientation of the shell are elucidated. The mode of life of the mollusk is specified. The influence of the theory on facts perception is shown.

Key words: Buoyancy, chambers, distribution and geological age, guard, keels, mode of life, origin, orientation of the shell, phragmacone, proostracum, Spirula L.

1. Introduction concern with the subject of work, were excluded. In spite of such limitation a number of facts, The spiral shell has been appeared many times unnoticed earlier, were found. It is natural that the during of different shelled . There signs, seeming negligible ones, acquire importance by are many foraminifers, sessile bristleworm Spirorbis; another putting of the question, and in contrary: the gastropods; some bivalves (Exogirus, Gryphea, consideration of question from a “conventional” jewelbox clams, the rudist Toucasia, the extinct standpoint could just obstruct or even to distort Pliocenian cockle Prosodacna and so on). facts—that will be shown below. This moment is not In external shell appears ever taken into account in the scientific periodic, independently in nautilids, ammonits and relying on authority of a specialist in such or another secondarily—in females of Argonauta. The results of branch. these processes are on hand: shell compaction as adaptation to the greater maneuverability (at the 2. Morphological expense of the speed). The other deal that on the way 2.1 Spirula and Familiar Forms to this solution was temporary rejection from active mode of life—pass from the straight shell to the bent Spirula is a relict with internal spiral one and only afterwards—to the spiral one. shell. Currently belemnite-like Belemnoseina with Even more problematic appears the postulated bent chambered part of the shell () are tendency of internal shell spiralization, whose clear accepted for the ancestral group. example is spirula. The given article provides Such a standpoint could not be based empirically: arguments in favor of the contrary standpoint. In in contrast from , which are guiding , contrast to lookthrough works, it represents no more belemnoseines are extremely rare, since their guard than spread out proof of the correspondent thesis. For consists not from the calcite, but from less stable this reason the author stands just on the certain aspects, [1]. The other deal intuitive ground: without pretending of the complete description of presence of specific endocochlear appendages in Spirula and familiar forms. Furthermore, in the course belemnoseines, permitting their approach with of arguments elaboration, those losing immediate ammonites, seems to be more important sign than spiral shape of shell, as was mentioned above,

Corresponding author: E. O. Heyfetz, independent appearing independently in different mollusc groups researcher, research field: paleontologyand hydrobiology. and a number of other shelled animals. Correspondent

The Origin of Spirula spirula (Linne, 1758) 31

Fig. 1 The origin of Spirula due to the current version.

32 The Origin of Spirula spirula (Linne, 1758)

Fig. 2 The shells of the families Belopteridae (A) Belemnopsidae (B) and Spirulirostridae (C)—from the “fundamentals of . version was defined also by opposite spiral orientation utile volume of the body cavity, and, in contrast, the (see below). production of phragmocone leads to insignificant Meanwhile, the normal tendency in the evolution of increase of spending on shell building and to mollusc with the internal shell is its reduction up to its reduction of the utile volume of cavity, aggravated in complete disappearance. Apparent exceptions, like the bent and spiral form by the bending of shell, guard, increasing material spending, decrease the whose alternative is a simple increase of the working volume, i.e. the force of buoyancy of phragmocone diameter, like in belemnites. Meanwhile, cephalopods’ shell. the most bent forms of belemnoseines (e.g. From the phragmocone function as such it was Spirulirostra) possess a massive guard, reducing the assumed that the process of internal shell spiralization assumed adaptation to zero. was connected with development of passive buoyancy Furthermore, guards of belemnoseines are means. This is the classical version of the sepiae sufficiently more changeable than the evolution [2] that obviously disregards with benthic (Fig. 2). mode of life of the majority of . Since natural selection preserves only favorable In addition, from all the standpoints the most changes, the guard would reflect evolutional tendency efficient mean to increase buoyancy would be the in the first turn. Meanwhile, as was said above, in the reduction of guard. First and foremost, it would give boundaries of suborder of Belemnoseina the guard significant economy of material plus increase of the does not show inclination to reduction. In such a way,

The Origin of Spirula spirula (Linne, 1758) 33 the conclusion about belemnoseines’ shell negatively: “…Among the most ancient coleoid there spiralization does not correspond both with relative are no one spirally coiled form. The impossibility of variability of its parts, and with needs of the molluscs. the coleoid origin from spirally coiled forms may be Both absence of any traces of guard and reinforced by logical arguments. in Spirula are not evident in favor of the accepted Proostracum—straight supportive structure, version. Questions about their traces were asked commeasurable by the length with the body—would repeatedly. Both Naef and Bruun emphasize that the not appear in animals with spirally coiled shell” [5]. juvenile Spirula completely lacks any traces of The spread objection as such is the evident about protoconch [2, 3]. Chun in after consideration of importance of the problem. The other deal, how lightful organ of Spirula initially accepted it for probative the arguments mentioned are. vestigial guard [4]. Later he established the real The internal shell bending in familiars of Spirula function of the organ that was interpreted before as an Bizikov considers as a juvenile adaptation to adheasing disc. Warnke and Boletzky (2009) accept planctonic mode of life [5]. for the remnant of guard a thin membrane, developing To this argument the mentioned contradiction on the ventral (i.e., anti-guard) side of initial chambers between the function of guard and phragmocone is of Spirula shell. applied. The robust capitulum, enveloping the first Bizikov elaborates the theoretical grounding of the phragmocone chambers from the ventral side (Fig. 3) current version. The author dwells on the question of is evident that the guard formation even preceded the coleoids’ origin from the spiral forms, and solves it phragmocone bending.

Fig. 3 The comparative shell morphology of and Belemnoseina.

34 The Origin of Spirula spirula (Linne, 1758)

Fig. 4 The pair of keels on the juvenile whorls of the shell of Spirula (drawn from the object).

In the process of further shell growth the Such a suggestion permits to look on the facts more sack, stretched on the phragmocone, lost the contact closely. Let us consider the shell, whose juvenile with its concave part and ceased to produce the guard bubble–like chambers differ so sharply from on the ventral side (Figs. 2 and 3)—in contrast to that barrel–like adult ones. On the internal (e.g. anti-guard) of belemnites. side of the juvenile there is a pair of keels with The given peculiarity is preserved also in furrow between them (like runners). Externally it belemnoseines with straighten shell and their resembles , nevertheless, considering descendants, true cuttlefishes, where bending of sections either samples with broken chambers it may phragmocone could not be obstacle for guards’ be easily ascertain that the given formations are development. This suggests that the straighten forms completely independent (Fig. 4). originated from the bent ones, and not on the contrary. In contrast to the guard of belemnoseines and Correspondingly, both absence of specific sepiids, that is no more than overflow, the keels are appendages, and the spiral shape of shell are clearly separated from the phragmocone. Appearing interpreted as the evidence of neothenic origin of the on the 2-nd chamber after protoconch they are mollusc [5]. smoothen towards 12-th, reaching 0.3 mm in height.

The Origin of Spirula spirula (Linne, 1758) 35

Fig. 5 Cross-section of the juvenile whorl. 24—ventral rib. From 2.

Due to their position and geometrically correct Naef—combination of membrane with keels. shape, they represent a kind of sheath that enveloped In such a way, the internal side of whorls, formerly external part of the previous whorl. contacting with previous ones, bears a whole number The given structure was not described in of evidences of its past significance, vividly showing details—that may be explained by its small size and that Spirula comes not from forms not with bent, but “obscure significance”. Naef restricts himself by with tightly spiral shell. mentioning of ventral rib of on the 2.2 The Ammonite Features of Spirula juvenile part of the shell [2], putting the drawing of first three chambers’ section, but with no detail A whole number of signs closing Spirula with description of the formation. ectocochlear molluscs are overlooked when it is Sometimes between the ventral sides of the considered from the standpoint of the current version. protoconch and the following chamber thin membrane Thus, the internal shell of Spirula is not inscribed in is preserved. It was described by Branco, 1880 and the contours of body, but is projected out on both Appelöf, 1893 and currently it was re-discovered by ventral and dorsal sides of the body. I.e., its diameter Warnke and Boletzky. The authors assume that just it together with covering skin is greater than that of the was described by Naef as the “rib”. As was mentioned body. Frequently shell breaches the skin and comes before, the attention to this structure is explained by out. its interpretation as a trace of guard [6]. It is likewise In the case of emergency Spirula retracts its head that the membrane represents a residual contact of the with extremities in the mantle that is closed by mantle first whorls, and the rib, described by valves (Fig. 7).

36 The Origin of Spirula spirula (Linne, 1758)

Fig. 6 Spirula, retracted the head, front view (from Bruun).

It is in to remember here classical to close the . reconstruction of Trauth, due to which ammonites Such a picture rejected Schindewolf on a single closed the shell aperture not by head lobe (as nautilids argumentum that mantle cannot synthesize do), but with mantle , complete simultaneously aragonitic shell and calcitic (anaptichum) or valved (aptychi). The elongated operculum3 [7]. Aptychi and anaptichi were living chamber of ammonits evidents is in favor of interpreted as jaws of ammonites that contradict both such a conclusion. By carnivorous mode of life it to the shape correspondence of these formations and corresponded to developed . In the retracted aperture and findings of typical cephalopod jaws in stage head was in the depth of shell and was not able the same specimens [2]. Spirula provides an additional

The Origin of Spirula spirula (Linne, 1758) 37 argument in favor of the classic version, and the letter independent way, as a result of phragmocone bending, confirms the ammonite origin of Spirula. opposite to that of ectocochlear forms. Nevertheless, coiling of the internal shell appears 2.3 Shell Orientation even more problematic. To all appearance, the One of the most important arguments against the orientation took place, and its causes must be affinity of ammonits and Spirula is the opposite investigated. orientation of the spiral. In the former it is pointed It may be remarked, first and foremost, that the from the stomach, in the second on it (exo- and shell orientation in typical ammonites and current endogastric whorls, correspondingly). Furthermore, is defined not by a physiology, nor by a the later orientation is similar with that of belemnites whim of mollusc, but rather, by buoyancy distribution. whose dorsal margin of shell was longer than the The same is right for endocochlear forms5. ventral one. Let us consider that the ancestor of Spirula, which Naef writes: “Hand by hand very strong ventral swimmed in the horizontal position, possessed, like curving of phragmocones goes, the penetration of ammonites, by a shell with exogastric (pointed on the belemnoid in the body of proceeded up to back) whorl. impossible degree” [2]. The adaptation to the more even distribution of Jeletzky, the supporter of “ammonoid” version, buoyancy became shell’s uncoiling with simultaneous indicates: “The presence of /protoconch features/ shift of the great diameter along the body axis (Fig. suggests closer relations /of sepiids/ to the 7A). As a result, the former center of buoyancy that (sic!) than to any other ectocochlian situated at the top of the external shell was shifted at order but derivation of the Sepiida from the 90o downwards, i.e., towards the aboral end of animal. Ammonitida is ruled out by the opposite direction of Furthermore, because instead of ectocochlear forms coiling (or curving) of their shells” [10]. the body of the mollusс did not loaded the living In such a way, it seems improbable that the chamber, the center of buoyancy has to pass additional complete spiral of the shell suddenly changed shift downwards, at the direction to the apperture (Fig. orientation4, and not developed gradually in 7A).

Fig. 7 Re-orientation of shell in Spirula ancestry.

38 The Origin of Spirula spirula (Linne, 1758)

Fig. 7B shows the buoyancy distribution in the the mollusc appeared not hereafter the Miocene. spiral shell before and after the reorientation. It is As regards to the current distribution of Spirula, yet necessary to take into account, however that the shell Naef supposed that it is distributed in all open warm of Spirula, though is not attached to the mantle sack seas of the world ocean [2]. This viewpoint is shared walls, newerthelss is accompased by the firm cartilage currently, despite significant correction, introduced by [5], preventing shell oscillations during change of an expeditions of Bruun. Perhaps just an inattention to animal course. the data that seemed to be collateral, took place. Thus, the overturn could happen before the Nevertheless, they permit to establish the age of complete formation of the whorl—or of the quite Spirula more exactly than remnants. strong cartilagious capsule. It should be mentioned that the correspondent The alteration of the shell position in the given case division in the account of Bruun is called is connected not with the natural selection, but rather, “Geographical distribution”, not, let us say, “Places of with the direct influence of mechanical factors. The catching” that imposes greater responsibility, in other deal is preservation of the correct spiral by the particular, relating the negative result. Here we must point of growth detorsion. The evident about the later rely on conscientiousness of the expeditions that is process is the position of . It is found, like in still the most authoritative source. typical ammonites near the ventral margin of the shell, As regards to the positive results, whereas expeditions but, because of the reorientation and detorsion near of “Challenger” (1872-1876), “Blake” (1877-1886), the inner side of whorl—not near the outer one, as in “Princesse Alice” (1886-1922), “Valdivia” ammonites. Perhaps, the detorsion proceeded quite a (1898-1899) catched one specimen, and “Michael Sars” (1904-1913)—eight individuals [3]—12 as whole; the long time; correspondent sides of mantle altered using of net for different depth, aimed for the given proportion of the shell synthesis rate, and the spiral aim, permitted the expeditions of Bruun on the vessels preserved the former direction. The analogous “Thor” (1909) and Dana to catch 193 specimen in examples are the gastropods that turn the shell during different areas of the world ocean. By this the the metamorphosis in the more pleasant position. In expedition of “Thor” catched only one individual. The Prosobranch snails (the group of Streptoneura) the expedition of “Dana”, 1920-1923; 1921-1922-1995; visceral sac is torsed, and nervous stems are crossed 1928-1930-1933 animals, and the expedition of (hence the name). In opistobranch and lung snails (the 1931—one individual again. group of Ethyneura) such a torsion disappears As may be seen from the map (Fig. 5), the area of completely by preservation of the shell orientation. Spirula is broken in tree parts. 3. Ecological In the Indo-Pacific the area embraces region of India and also—of Northern and Eastern Australia. 3.1 Definition of the Geological Age of Spirula Near the coast of the Indian ocean of Africa Spirula The fossil remnants of Spirula were found in was not catched. The catches in the Pacific coasts of Miocene, i.e. sufficiently later after of the the America’s were not made—besides the gulf of typical ammonites. It is clear that its shell, thin and Panama (where abundant deep catches were) and the devoted of the appendages, have the least chance to be Marquese islands [3]. Correspondingly in the shell preserved than belemnoseines (as were said above, collection that I studied, a whole number of points in rare fossils), found a little bit earlier, in Eocene. I.e. American coast belonged to Atlantics only (i.e.—in the fossil shells of Spirula may be evident only that geographical order—Texas, Florida, Brazil,

The Origin of Spirula spirula (Linne, 1758) 39

Fig. 8 Catches of Spirula by expeditions of Bruun: A—positive; B—negative results (from Bruun).

Fig. 9 The disposition of continents and oceans in the late (from Gorodnitsky, Sonnenstein and Mirkin).

Barbados), whereas shells from the Pacific coast of N. America has been separated from northern the continents were absent. in Miocene, the geometric correspondence between The Atlantic distribution of Spirula is of peculiar African and American areas permit to suggest that in interest. Here it is found near the former mouth of the Atlantical region Spirula appeared before the final Tethys—in the north part of the Atlantic coast of Africa separation between the latter continents that proceeded (from Gibraltar gulf up to the middle of Mauritanian in the [11]. Absence of populations projection), and also in the correspondent huge outside of these regions is also remarkable. This may excavation near the coasts of the Americas (Mexican be connected, perhaps with changes of biocenosis in gulf and Caribbean Sea). Though the northern part of the process of the Atlantics formation.

40 The Origin of Spirula spirula (Linne, 1758)

The absence of Spirula catches between the enclaves specimen, as the former is pointed upwards, whereas mentioned suggests that the center of Spirula origin eyes look at side. Not too much improves the situation was Tethys that connected the areas. The later ocean both the normal orientation. In this case Spirula would existed from the till Oligocene (Fig. 6). see deepened organ of the other individual only in the In the later Oligocene Tethys ceased connection case, when their positions are mutually perpendicular, with the Indian Ocean [12], whereas connection with and eye of the given individual is found directly the Atlantics desisted in Maastricht, i.e. in the late against the aboral end of the other one. It is sufficient Cretacious [13]. The remnant of Thetys, the ancient to orientate itself by a ray of light. In favor of this Mediterranean basin, was practically extinct in the assumption telescopic eyes, permitting to define weak Messinian crisis, i.e. in the late Miocene. At this time changes of illumination degree. vanished the local population of Spirula, whose shells Orientation of carnivorous animals (in private, are found in the Miocene of the Italy [2]. The tunes often attack the Spirula) by such a secret lantern shallow-water Gibraltar gulf currently is the obstacle is difficult. Thus, by enemy approach Spirula retracts on the molluscan migration in the Mediterranean Sea. in mantle and turns in vertical position, excluding the In such a way the data of Bruun expeditions permit lightful organ from the field of carnivorous sight. to suppose that Spirula are the relict of the Tethys, and The aforesaid assumption may be checked by its age is limited by the beginning and the end of immediate observation. Jurassic period of Mesozoan era. In the theses, published in the materials of Malacological society, 2002, the lightful organ 3.2 Function of the Lightful Organ erroneously was called “luminophore”. Anistratenko In accordance with the version about development V. V. (Institute of zoology n. a. I. I. Schmalhausen of the passive floating mean Spirula was treated NAS of Ukraine) mentioned that the accepted term is repeatedly as bearing a passive mode of life. The “”. morphology of lightful organ6, whose function The correspondent roots came from Greek words appropriately is claimed to be mysterious, is evident “φως” (genitive “φωτος”) and Latin “lumen” that in against such a version. both cases implies “light”. Nevertheless the first root Situating on the aboral side of the body, i.e. on the mostly relates to the light, coming from the external maximal distance from both eyes and tentacles it source: photoreceptor, photosynthesis, whereas the clearly does not serve illumination of the field of sight second one—to the light, emitted by organism itself: or as prey bait. It did not aim for defense against bioluminescence, luminescent organisms etc. In such a enemies (For this purpose some cephalopods ejaculate way, the term “photophore” appeared because of blinding luminous ink, whereas other ones disorient imperceptions of etymology hence it favors to an enemy by illumination of stomach on the confusion and encourages pedantism that gives background of bright sky). The visibility of the preference of training before intelligence. I propose to lightful organ, found in the sucker-like pad, is too correct the inexactness committed, and to replace the restricted. term “photophore” on “luminophore”. It is likely that such an organ serves as the mean of 3.3 The Mode of Life of Spirula distant signalization. In private, such a function assumed Broon. It is considered that in the natural conditions In the vertical position, prescribed for animal, Spirula Spirula swims in the vertical position head downwards, just will be unable to see the lightful organ of the other in accordance with the buoyancy distribution, hence, it

The Origin of Spirula spirula (Linne, 1758) 41

Fig. 10 Text with description of Spirula movement in the aquarium (from Bruun). is not able to make the normal movement. Such a These rushes were generally made by “backing”, i.e. conclusion disagrees with sociability of the mollusc, the animals moved with its hinder end forward, having as like as possessing of the lightful organ, helping first “reversed the funnel so as to torn its opening such a habit. forward, towards the head , at the same time flattening The current concept is based by immediate the fins close into the posterior end/withstanding with observations, provided by Danish scientist A. Bruun the declining force of the shell buoyancy by funnel in the aquarium on the investigatory vessel “Dana” only/… Less frequently Spirula was observed in the (1921-1922 and 1928-1930). Spirulas survived in the aquarium making a forward rush with its head to the aquarium up to 48 hours. As was mentioned above, front” [3]. the catch formed 193 individuals. It is clear that the observations mentioned disagreed Coming to conclusion about the active mode of life with well based version of the origin of Spirula. From of Spirula, the author assumed that the current version the other side, the grounding of the expedition of is connected with non-critical relation to the Bruun leaves no doubts whatsoever. As a result the conditions of observation. Really, Spirula was text was unwittingly conformed to the theory via withdrawn from great depth, suffered temperature missing of the “excessive” fragment. choke—refrigerator chamber on the vessel was absent, Due to the description provided, Spirula nowhere and the water warmed up to the temperature of air; the near looks like passively floating animal with reduced molluscs passed through a layer of stinging muscles (like -bathyscaphe Cranchia). Being the coelenterates, the external layer of mantle was perfect swimmer it is forced to overcome the surplus damaged etc. [3]. buoyancy of shell. In this situation the guard will not Nevertheless, turning to the text I discovered that be the unnecessary ballast. Both its absence, like the spirulas hanged downwards in the first minutes of the spiral shape of the shell is primitive signs, inherited observation, before they completely recovered from from ectocochlear ammonites. choke. Afterwards the following description Correspondingly, the passive defense of Spirula seems mentioned: “Like other cuttle- Spirula often makes not the newest adaptation, but rather, the inheritance swift jerky movements, dashing off suddenly in any of ancestors, like the ability of motile and snappish direction: upwards, downwards, or from side to side. soft-shelled turtles to retract the head into the shell.

42 The Origin of Spirula spirula (Linne, 1758)

The mentioned prototypical features of Spirula The base for both closing of Groenlandibellids with permit to receive idea about appearance of ammonits Sepiids, and rejection of belemnite origin serves the that give a base to consider it as the specialized protoconch, plunged by thin prosiphon and blind representative of the given subclass. At the same time encapsuled outgrow of the siphon, caecum [10]. In Spirula possesses such newest adaptation as muscular contrast, protoconch of Belemnitida, Aulacoceratida mantle and fins. In such a way, it represents a and Phragmotheutida is separated from phragmocone transitional link between the most important stages of by secondary membrane—probably, larval adaptation the cephalopod evolution. for the buoyancy stabilization (Figs. 1 and 2). As regards ammonites, they do not represent a blind “It is impossible to assume that the caecum and branch, ending with Spirula. Cuttlefishes, prosiphon could reappear in the Sepiida after having and myopsid squid are closed to the latter, in contrast been completely lost by alleged belemnitid ancestors to the oegopsid that could be descendants of which there fore must be rooled out as root stock of belemnite-like forms. Sepiida” [10]. Meanwhile the given sign is prototypical one, i.e. it 5. Comments characterizes not the degree of closeness of (1) In the given article possible evidences about Groenlandibellids with sepiids, but the stage of origin of other from spiral forms (such as “belemnitization” of both groups. In contrast to the bending of the top of phragmocone in belemnite indication of Jeletzky, the protoconch structure by Pachytheuthis, ventral grow of belemnite guard, itself cannot exclude the sepiid origin from primitive planispiral top in recent squid Hystiotheutis) belemnite ancestors with the plunged protoconch. are not discussed. This subject requires a separate The most important feature, however, is the guard consideration. morphology, because it does not restrict to one-time (2) Starobogatov (1976) placed belemnite-like larval adaptation, but requires alteration of substances’ familiars of Spirula in suborder Belemnoseina [14]. exchange during all the life of the organism. The The author of the current article keeps such a guard of Groenlandibelus, like that of belemnites is subdivision. composed of calcite and possesses typical The subsequent discussion showed that the belemnite-like structure [10, 15]. In such a way, signs proposition of Starobogatov was not accepted by the of Groenlandibellid cannot form a base for separation current scientific society. The base of the current of sepiids and belemnitids. classification forms the system, proposed in the It is obvious the reduction to naught of the guard monography of Jeletzky, 1966. The of morphology as the criterion of closeness and, in Groenlandibellidae is affixed to the order of Sepiida, contrary—hyperbolization of the protoconch whereas the origin of the later from belemnites is significance with its carving out from the evolutional rejected. context (in private, factual rejection of possibility of Groenlandibellids are characterized by narrow closed protoconch evolving from a plunged one). straight phragmocone and needle-shaped proostracum It seems that the cause of such an approach is rooted (Fig. 1). The guard is either vestigial (Groenlandibelus) in the aspiration to close Spirula with ammonites (that whether absent (Naefia). The forms are similar with requires its separation from the belemnite stock). true belemnites. Thus, Groenlandibelus was described Jeletzky emphasizes the affinity of sepiids and initially as the representative of the ammonites, but he is forced to deny direct origin [15]. because of the opposite whorl orientation. Furthermore,

The Origin of Spirula spirula (Linne, 1758) 43

Fig. 11 Phylogeny of Spirula and related forms (according to the article).

44 The Origin of Spirula spirula (Linne, 1758)

recognizing that the features of protoconch are provided by representatives of the classic version [1, prototypical one, thus, “can be inferred” in the 2]. assumed orthoconic ancestors of belemnites; Jeletzky, In such a way, the spread of the Spirula relationship nevertheless, calls the “sepiid” protoconch at the expense of orthoconic (and/or planctonic) forms “ammonite-like” [10]. seems not well grounded, though fitted in one of the The following step in this direction was made by consistent schemes. Reitner and Engeser in 1982. The authors derive the From the concepts mentioned it follows the order of , including Spirula, importance to put the question about the internal spiral groenlandibellids and belemnoseines (sensu shell origin, and equally—of its proper solution. Starobogatovi) immediately from . The */The asterisk refers to previous comment as the conclusion grounds not on the shell spiralization, subcomment/There are, in private, flattened, open on since the Groenlandibellids are considered as the root the ventral side phragmocone; papillose dorsal surface; group, but only on the morphology of protoconch weakly developed guard, hence, the similar mode of mentioned. life. The name of the order (about Heckel, 1896) (3) At the last time the version appeared, due to converts so important sign, as spiralization of which lower jaw could perform as a shield, closing the phragmocone in the pure formal denomination. shell aperture [17]. The given conclusion seems to be N. b. the correct bringing of the Spirula to symptom of theoretization decline, when synthesis of ammonits supposes it placing in the separate order, facts is substituted by that of authorities’ statements. more exactly, exclusion of belemnoseines and, For acceptance of such an exotic hypothesis more furthermore, groenlandibellids from the order, bearing ponderable arguments are necessary than an its name. impossibility of simultaneous synthesis of calcite Both the superorder Spiruloidea, established by operculum and aragonite shell by the same organ Bizikov, raises questions. (mantle) that may be refuted by comparison with To this division are jointed recent deep-water squid belemnites, whose mantle produced both, aragonitic order Chirotheutida because of their gladius similarity phragmocone and calcitic guard. with phragmocone of groenlandibellids [5]; whereas (4) Indeed, it may be pointed to the turnover of the the former pivotal group—the order Sepiida is shell during gastropod metamorphosis. Reorientation excluded [5]. may appear also as the result of exchange of the shell Similarity of cuttlefishes with Jurassic rate between the opposite its sides—in the quite trachitheutids* on which Bizikov refers (ibid), if does common sinistral snails (Physa, Lanistes, Clausilidae not the result of convergency, then, in any case does etc.). The analogous examples in cephalopods were, not contradicts by sepiid origin from spirulids. perhaps, anomalous ectocochlear ammonites The evidence in favor of the latter is the plunged Climeniida (), whose siphuncle was protoconch—the only base for groenlandibellids and positioned near the inner (not outer, as in typical belemnoseins’ incorporation in the single order; ammonites) part of whorl. If this is the case, the characteristic for belemnoseines appendages (wings) upturned part, in contrast to that of snails, was not the and also—germinal (or vestigial) shell spiralization. It shell (whose position was defined by buoyancy), but is necessary to remind also about argument of direct the ventral and the dorsal sides of the soft body. similarity of Spirulirostrina (Belemnoseina) with (5) Correspondingly, the shell of belemnites was sepiids and Belosaepia (Sepia)—with belemnoseines, found in the most stable position. The longitudinal

The Origin of Spirula spirula (Linne, 1758) 45

Fig. 12 Distribution of buoyancy in shells of belemnite-like cephalopods. section of the phragmocone looks like rectangular References triangle, whose hypothenuse is represented by the [1] Крымгольц Г. Я., Sepioidea//Основы палеонтологии. dorsal, and the greater, real cathetus—by the ventral Моллюски — Головоногие, ч. II,/ под ред. Орлова Ю. side that lied, in average, near the horizontal position. А., М.; Гостехиздат, 1958.—359 с—c. 162–168. The second, imaginary cathetus—is the line stretched (Krymholz G. Ya., Sepioidea//Fundamentals of paleontology. Molluscs—cephalopods, p. II/edited by from the extreme points of the sides—the diameter of Orlov Yu. A., Moscow, Gostekhizdat, 1958. p. 359. in the aperture. The center of buoyancy passed through Russian). bisectrix of the angle between the sides. The lines of [2] Naef, A. 1922. Die Fossile Tintenfische, Verlag Gustav hypotenuse, i.e. of the dorsal side and bisectrix were Fischer, Jena, p. 322. [3] Bruun, A. 1943. The Biology of Spirula Spirula. pointed obliquely upwards, whereas in the case of the Dana-Report, p. 44 Available at site: opposite orientation—obliquely downwards. Shift of //rogov.zwz.ru/bruun,%....ula.pdf. the line, connecting the centers of buoyancy, in the [4] Chun, K. 1903. Aus den Tiefe des Weltmeeres, Jena, horizontal plane was impeded by both, position of the Fischer, 591 s. [5] Бизиков, А. В., Эволюция формы и функции body and gravity of the guard. раковины головоногих моллюсков подкласса Acknowledgments Coleoidea, Автореферат диссертации на соискание ученой степени доктора биологических наук, М. 2008 I began to work on this article in Israel, where I — 52 с. Размещен на сайте (Bizikov A. V., Evolution of shape and functions of shell of cephalopod molluscs of spend few . The valuable help put the members the subclass of Coleoidea, author’s abstract of of Hebrew University of Jerusalem, Prof. J. Heller and dissertation for inception of scientific degree biological doctor H. Mienis and the member of Geological science doctor, Moscow 2008, p. 52, in Russian. Survey of Israel Prof. Z. Lewy, Painter-animalist W. [6] Warnke, K. M., and Boletzky, S. V. 2009. “The ‘Ventral Rib’ of the Shell in Spirula (Cephalopoda, Coleoidea): A Fergusson consulted by figuration of drawings. Cryptic Guard?” Berliner paläobiologische To all them I express my true thanks. Abhandlungen 10 (11-11): 357-9.

46 The Origin of Spirula spirula (Linne, 1758)

[7] Lehmann, U. 1982. The Ammonites. Their Life and Their [13] Свиточ А. А., Сорохтин О. Г., Ушаков С. А., Forms. Cambridge: Cambridge University Press, p. 466. Палеогеография, М., Academia, 2004—448 с. (Switoch [8] Друщиц В. В., Догужаева Л. А. Аммониты под A. A., Sorokhtin O. G., Ushakov S. A., Paleogeography, электронным микроскопом. М.; МГУ, 1981.—240 с. Moscow, Academia, 2004 p. 448, in Russian). (Druschitz V. V., Doguzhayeva L. A. Ammonites under [14] Старобогатов Я. И. 1976. Основные особенности the electronic microscope, Moscow, editory of Moscow филогении головоногих моллюсков и вопросы их State University, 1981 p. 240. in Russian). системы. В сб.: Тез. Докл. Совещ. по пробл. [9] Lewy, Z. 2000. “Nevertheless, Aptychi Are Ammonoid «Основные проблемы систематики животных». М.; с. Opercular Plates, Geological Survey of Israel.” Current 17-22. (Starobogatov Ya. I. 1976 Main peculiarities of Research (12): 155-8. cephalopod mollusc phylogeny and questions of their [10] Jeletzky, J. A. 1966. Comparative Morphology, system. In Transact: Thes. Rep. Counc. by Probl. “The Phyllogeny and Classification of Fossil Coleoidea, The main problems of animal systematics”. Moscow; pp. University of Kansas publishers, p. 162. 17-22. [11] Городницкий, А. М., Зоненштайн Л. П., Мирлин Е. Г., [15] Birkelund, Т., and Hansen, Н. J. 1974. Shell Реконструкция положения материков в фанерозое, М. Ultrastrucures of Some Ammonoidea and Наука, 1978. —121 c. (Gorodnitsky A. M., Zonenschtein Coleoidea and Their Taxonomic Implication. L. P., Mirlin Ye. G., Reconstruction of the continents Munskgaard, København, pp. 34, + 15 plates. position in the Phanerozoe eon, Moscow, Nauka, 1978 p. [16] Reithner, J., and Engeser T. 1982. “Phylogenetic Trends 121 in Russian). in Phragmocone-Bearing Coleoids (Belemnomorpha).” [12] Леонов Г. П., Историческая геология, М., МГУ Neues Jahrb. Geol. Paläont. 164: 156-62. 1956—363 с. (Leonov G. P., Historical geology, Moscow, [17] Lehman, U., and Kulicki, C. 1990. “Double Function of editory of the Moscow State University 1956 p. 363, in Aptychi (Ammonoidea) as Jaw Elements and Opercula.” Russian). Lethaia 23: 325-31.